Coating apparatus and method



July 15, 1941. J. D.. MURRAY COATING APPARATUS AND METHOD Filed Jan. 9, 1940 3 Sheets-Sheet l gwpczm tm /o/m D.- Murray A Sbtocmmg.

July 15, 1941. J. D. MURRAY I CDATING APPARATUS AND METHOD 5 Sheets-Sheet 2 Filed Jan. 9, 1940 1111M: O VHO FT g. 117

y 1941- J. D. MURRAY 2,249,088

COATING APPARATUS AND METHOD Filed Jan. 9, 1940 3 Sheets-Sheet 5 Patented July 15, 1941 COATING APPARATUS AND METHOD John D. Murray, Chicago, 111., assignor to The Liquafilm Corporation, Chicago, 111., a corporation of Illinois Application January 9, 1940, Serial No. 313,135

30 Claims.

This invention relates to methods and apparatus for coating surfaces of sheets and webs of paper, fabric and the like and is more particularly concerned with methods and apparatus for applying and distributing coating material upon said surfaces to obtain a uniform finish thereon.

This application is a continuation in part of my co-pending application Serial No. 231,102, filed September 22, 1938.

In coating said sheet or web surfaces, the invention involves novel methods and apparatus for applying and distributing uniform deposits of coating material thereon. It is immaterialto the practice of the invention whether these partially or wholly impregnate the same.

The disclosure of the preferred embodiment of the invention in the present instance will be specifically directed to the coating of surfaces of sheets or webs of paper, fabric, or the like with thermoplastic coating materials which are normally solid, such as solid lacquers, or resins and the like which are melted for application to the surface, although the invention is not so limited.

Coating methods and apparatus in general use today for applying liquids and solvent plastic materials to sheet or web surfaces have not proved successful for applying melted plastic material, especially at high web speeds. These meltedplastic materials harden almost instantly when they are deposited and previous attempts, of which I have knowledge, to spread these coatings during and after deposit have resulted only in incomplete, non-uniform, streaky and uneven coatings.

Moreover, in prior coating methods the material is deposited upon the sheet or web surface without accurate control'over the amount applied or the uniformity of the deposit. Besides being slow, therefore, prior methods and apparatus are expensive in that they waste coating material, because in order to insure complete coverage of the surface it is usually necessary to apply an excess of material, the apparatus being incapable of providing thin uniform coatings.

With these defects of the prior art in mind, it is a major object of the present invention to provide novel methods and apparatus for speedily applying thin coatingsof accurately measured and controlled quantities of coating material, such as thermoplastic coating compositions of various types, upon sheet or web surfaces or the like in a thin uniform coating.

A further object of the invention is to provide novel methods and apparatus for coating a sheet a coating of desired thickness is deposited upon the surface. Preferably, I employ an accurately made deposit roller having localized, closely adjacent, shallow recesses arranged in a uniform pattern upon its peripherial surface for depositing the material.

It is a further object of this invention to provide novel methods and apparatus for coating a sheetsurface or the like wherein controlledquantities of thermoplastic coating material are deposited upon the surface in a uniform pattern of mounds, ridges or the likeso arranged that when subjected to sufficient' heat and directional pressure the deposited quantities flow and are leveled in a direction substantially opposite to the direction of travel of the surface, and are fused or leveled into a smooth uniform coating. A further object of the invention'is to provide novel apparatus and methods for coating and glossing or finishing sheet surfaces or the like upon which thermoplastic material has been deposited in a uniform pattern, wherein the surface is progressively passed over a smooth heated blade face having a substantial area of contact therewith under pressure and then over a flexible straight smooth edge at an angle selected to give a predetermined flnish to said surface. If desired, the coated surface of the sheet may be exposed to additional heating means such as a radiant heater or the like and automatic heating controls may be employed for maintaining the deposit apparatus, the smooth face and the flexible edge at desired temperatures.

A further object of the invention is to provide a novel method and apparatus for coating a sheet 40 surface or the like wherein a surface upon which over the smooth flexible straight terminal edge of the blade at an angle selected to give a predetermined flnish to said surface. Specifically a heated smooth arcuate surface which serves as a backing for the bade as it bends in response to pressure of the sheet and acts as a heating medium for insuring that the smoothing portion of the blade is maintained at high temperature is provided.

Further objects of the invention will presently surface or the like which comprises depositing appear as the description proceeds in connection with the appended claims and the annexed drawings in which:

Figure 1 is a side elevation of a coating machine embodying the principles of the invention for applying thermoplastic coating material to a travelling web of paper or the like;

Figure 2 is a top plan view of the machine of Figure 1 illustrating mainly the roller arrangements;

Figure 3 is an elevation of a mechanically grooved roller used for depositing the thermoplastic material. The surface of the roller has been greatly enlarged in two places to show optional desirable groove formations;

Figure 4 is an enlarged side elevation partly in section illustrating the details of the blade holder and its adjustment, and also the manner in which the blade is medially supported and heated when it is bent over by the web.

Figure 5 is a fragmentary front view partly in section illustrating further the blade holder adjustment;

Figure 6 is a section taken along line 6-4 of Figure 5 illustrating further the blade support construction;

Figure 7 is an exploded view partly in section of the flexible blade holder;

Figure 8 is an elevation of the blade illustrating the enlarged apertures through which the blade holder clamping bolts pass and which permit expansion of the blade without distortion at the holder;

Figure 9 is a fragmentary view illustrating a further embodiment of the invention wherein the flexible blade is not medially supported;

Figure 10 is a fragmentary sectional view of a further embodiment of the invention wherein the coating deposit roller is a smooth surfaced cylinder provided with an axially reciprocable serrated doctor bar; and

Figure 11 is a fragmentary front elevation partly in section illustrating further the doctor bar of Figure 10 and the uniform sinuous pattern of coating material which it provides on the coating deposit roller.

Coating deposit apparatus Referring to Figures 1 and 2, the entire apparatus is supported upon a base I I bolted or otherwise secured to the floor or some rigid support. At opposite sides, base II is provided with upstanding walls IZ.

A coating deposit roll I3, having a uniform pattern of surface recesses of uniform depth as will later be described, is provided with reduced end portions H journaled in walls I2 and rotates about a fixed axis. A parallel impression roll l5, surfaced with rubber or any suitable resilient material which can withstand the high coating deposit temperatures employed, has reduced end post II is manipulated to space rolls l3 and II.

Driven roll I! and impression'roll I! rotate in opposite directions at equal peripheral speeds.

The lower peripheral surface of roll I! is submerged beneath the level of a quantity of melted thermoplastic coating composition 24 in a container or pan 2!. Container 2! is provided with an electrically heated plate or some equivalent manner of maintaining the melted material 24 at a desired high temperature.

As shown in Figure 1, roll I! rotates in a counterclockwise direction and, as its peripheral surface emerges from the coating bath, excess coating material is wiped off by a suitable flexible doctor blade 26 mounted in a heated support 21. Support 21 is adjustable about the axis of its supporting stub shafts 2| for varying the pressure and angle of contact of the doctor blade with the peripheral surface of the coating deposit roll. Since doctor bladefii is preferably of the usual adjustable, reciprocating type employed in intaglio printing apparatus, further description of The surface of coating deposit roll I! is provided with a uniform pattern of shallow, localized, closely adjacent recesses, which may be grooves or pockets of any desired shape, of uniform size.

Employing conventional etching methods such as are used in forming intaglio printing cylinders, it is not possible to controlthe depth of etch with such accuracy as to obtain shallow recesses of uniform depth on the roller surface that will provide uniform very thin coating .deposits. I have discovered that it isnecessary to very accurately cut, impress, or otherwise mechanically form these recesses by means of knurling, milling, or like machine tooling to gain the desired accuracy and uniform depth of recess necessary to deposit measured controlled quantities of material for providing very thin uniform coatings on web or sheet surface.

The forms of coating rolls that I first utilized for this purpose are illustrated in Figure 3. At the left side of Figure 3, the roll surface is formed with a parallel series of narrow, generally V- shaped grooves 28 of uniform size, depth and spacing, equally spaced by ridges 2!. While grooves 28 extend substantially longitudinally of the roll surface, they are not parallel to its axis all; are arranged at an angle with respect there- My first coating deposit roll had its surface grooves arranged at an angle of about 2% degrees to the cylinder axis, and the grooves had a uni- Recesses I! are preferably bridged by bars I! v through which pass threaded adjustment posts 2| whose lower ends are seated in blocks ll.

Posts II are provided with operating handles 22 form depth of about .015 inch and a spacing of about .045 inch.

Another early form of deposit roll is illustrated at the right in Figure 3, where a fine spiral circumferential surface groove 3| or thread of very small pitch extends from one an of the roll to the other. This groove had a dep h of about .001 inch and due to its pitch is inclined-about 89% degrees to the cylinder axis.

The above described early forms of coating rolls were operable for depositing uniform quantities of coating material upon low speed paper webs, but were not commercially practical for the thin coating of high speed webs. The longitudinally grooved roll deposited too much material, about forty to sixty pounds per ream of paper, while the spirally grooved roll embossed the paper and even cut it during high speed erations.

Coating operations and tests employing the above described rolls, however, clearly demonstrated the operation and basic principles of the invention; and improved rolls embodying these basic principles and developed to suit practical high speed thin coating web conditions have since been made and are described and claimed in the co-pending applications of myself and Russ B. Leech, Serial No. 260,188, filed March 6, 1939, and that of Russ B. Leech, Serial No. 272,526, flied May 8, 1939. I

Roll I3 is preferably heated and maintained at a constant temperature by means of an internal, thermostatically controlled electrical heating system (not shown) so that the thermoplastic material on its surface will be maintained in fluid state until deposited.

Web guide apparatus-coating station An idling guide roll 33 whose opposite ends are rotatably supported in a pair of paralled arms 34 screws 48. Each blade holder 41 is secured as by bolts 49 upon a support 52 provided with an apertured boss fitting over the'adiacent end of bar 46 inwardly of the frame and is non-rotatably secured thereto by set screws 5|. .Bcrews 48 afford a means for adjusting the blade as will be described later.

Referring to Figures 4-6, each blade holder 41 comprises a support 52 substantially L-shaped in cross section and having opposite rigid end walls 53. The inner surfaces of member 52 serve as guides for a slidable block 54 through. which passes in threaded engagement an elongated threaded rod 55- provided with enlarged collars 56 rigidly secured thereto for engaging the inner surfaces of end walls 53. At opposite ends, rod 55 extends through walls 53 and is provided with screw-driver slots 51 or similar means for enabling extending rearwardly from a bar 35 to which they are non-rotatably secured, as by set screws 36, is provided at the web entering side of the coating station. The opposite ends of bar 35 are journaled in bosses on walls l2 and maintained against rotation by means of set screws 31.

When it is desired to adjust guide roll 33 to alter the tension of the web, or to insure that the web approaches the pass between the deposit couplerolls at the proper angle, screws 31 are released to permit rotation of bar 35, the bar is rotated, and the screws then tightened to maintain the guide roll in adjusted position.

At the other side of the coating deposit. station, a second idler guide roll 38 has its opposite ends rotatably mounted in a pair of arms 39 extending from a transverse bar 4i. Arms 39 are nonrotatably secured to bar 41 as by screws 42. The opposite ends of bar 4| are. mounted in suitable rotatable supports in walls I2 and are maintained against rotation in a desired adjusted position by suitable screws 43.

Coating levelling and smoothing apparatus Beyond the coating depositapparatus above described, is a levelling and smoothing station, illustrated at the left side of Figure 1 and supported upon forwardly projecting rigid frame portions 44 which may be bolted to or made integral with walls l2.

Extending between frame portions 44 and having its opposite ends non-rotatably afllxed thereto is a stationary steel cylinder or backing shoe 45 whose arcuate peripheral surface is polished or otherwise treated to make it as smooth as possible. It is not necessary that shoe 45 be a complete cylinder and it may be arcuate over only such portion as is necessary to back the flexible smoothing blade as will presently appear. Cylinder 45 is preferably provided with internal heating elements such as electrical coils and the like (not shown), or is heated by steam for a purpose later to be described.

Rearwardly ofcylinder 45 and below the web, a rigid bar 45 extends between frame portions 44, and at each end of this bar is provided a blade holder support generally designated at 41 in Figure 1 and illustrated in enlarged scale on Figures 4-6 As illustrated in Figure 5, the opposite ends of bar 45 are mounted for rotatable adjustment in frame portions 44 but held against rotation by the attachment of a suitable tool. When rod 55 is rotated, as was screw-driver inserted in slot 51, there is no axial movement of screw member .55 due to enlarged collars l5 and block 54 is displaced vertically along its guide.

Smoothing blade 53 is a wide, thin, flexible and springy sheet of steel or the like supported along one edge by a blade holder'and having its opposite free end terminating in a straight, true edge which may be ground, honed or otherwise sharpened as desired. A practical blade which has performed satisfactorily at web speeds up to '70 feet perminute is about'.003 inch thick. This thickness may vary in accordance with web speeds and tension. In general, for higher web speeds, thicker blades are employed and for lower web speeds, more springy, thinner blades are employed. Blades having thicknesses of about .006 inch have been successfully employed. If desired, a back up blade, identical with blade 58 but about an inch shorter may be mounted in the same holder with blade "but onthe side opposite the coated surface. I

The blade holder comprises rigid flat bars 59 and 6!. Bar Si is provided with projecting dowel pins 52 and threaded apertures 53 which are aligned with corresponding apertures 84 and 55 on bar 59. Bars 59 and Glare each provided with linings of some heat insulating material 50, such as an asbestos composition, to keep them outof metallic contact with the blade and thereby prevent heat from the blade from being convided, or during assembly of the blade holder and blade, screws 55 are tightened only enough to loosely hold the edge of blade 48 between straps 58 and GI. In practice, I have covered that best results areobtained when t e blade may be easilyshifted back and forth in its holder by means of the hand of the operator. ,Slots 61, in a practical blade which has proved successful, are designed to permit a'total endwise movement of the blade in its holder of about V4 01 an inch and a total up and down movement of about 3*; of an inch. I

If the blade is clamped tightly, expansion when heated causes its free flexible edge to warp and buckle. The above described loose support and the slots 51 permit unrestricted expansion of the heated blade, and the heated smoothing area and glazing edge of the blade remain straight and true without deformation during operation.

The blade holder is rigidly supported at opposite ends by removable fastening means such as bolts 58 passing through blocks 54 and bar 5|. Bolts I do not contact the blade and therefore do not interfere with the above described loose support for the blade.

When there is no web passing through the machine. blade 58 maintains itself in a substantially vertical position as shown by the dotted lines in Figure 4. When, however, a web under tension is being coated and smoothed, pressure of the web bends the blade in the direction it travels to the full line position of Figure 4. The arcuate backing surface of cylinder 45 serves as a source of heat and a medial support for the blade. If desired the blade holder may be heated to insure against loss of heat by conduction.

The degree of contact of blade 58 with shoe 45 and the angular relation of the blade with respect to the shoe may be regulated as desired by means of the adjustments provided at 48 and 51.

When exceedingly springy blades are employed at 58, some dimculty may be: experienced due to excessive-vibration at the free edge of the blade. To overcome this difficulty, a rotatable vibration absorbtion roll 59, preferably surfaced with a rubber blanket or the like, may be arranged to contact the uncoated surface of the web just above the free edge of the blade. The sole function of roll 59 is to restrain and dampen blade vibration and care should be taken that it does not clamp the web on the blade surface or inter.- fere with free bending of the blade in response to tension changes in the web.

To secure proper adjustment of roll 59, its opposite ends are rotatably mounted in blocks 10 (Figure 1) which are slidably mounted in a cut out portion at the upper edges of frame portion 44 and provided wtih threaded adjustment screws H. Suitable compression springs 12, be-

tween the bottoms of blocks Ill and the recesses,

are provided for insuring upward vertical movement of the roll 59 when it is desired to displace it away from the blade edge.

In most instances, however, roll 58 may be eliminated entirely since, with a. uniform web speed and a properly mounted blade, there is very little tendency of the blade end to vibrate excessively.

Beyond the smoothing station, an idler guide roll 13 is rotatably supported at opposite ends in arms 14 projecting from a bar 15 and non-rotatably secured thereto, as by set screws 18. Bar '15 in turn is rotatably supported at opposite ends in frame portions 44, but is held against rotation by suitable set screws 11. V

Adjustment of roll 13 by rotating bar 15 about its axis effects an adjustment of the angle with which the web leaves the free edge of blade 58. This adjusted position of roll I3 may be locked to gain any desired angle, and consequently to secure the desired surface finish or glaze n the coated web, by means of screws 11.

Doctor blade holder 21, deposit roll it, cylinder 45 and all other heated members in the apparatus are preferably heated by electrical elements controlled by suitable thermostat switches to maintain desired surface temperatures.

As illustrated in Figure 1, a radiant heater 85 having a reflector t and a plurality of electrically energized coils or element 51 may be provided Figure 1.

Operation Web 8, usually paper, is led from a supply roll on a suitable stand (not shown) over guide roll 33 and between coating deposit roll I3 and impression roll l5. Since rolls l3 and l5 are driven at the same peripheral speed, there will be no relative slippage between their surfaces and either surface of the web to be coated. Web S is under tension and traverses the coating pass rolls l3 and II with its opposite surfaces substantially tangential thereto and in substantial line contact therewith.

Thermoplastic coating material is placed in solid state in pan 25 and heated so as to maintain it in a fluid state. As roller I 3 rotates in a counter-clockwise direction in Figure 1, surface blade surface.

grooves 28 become filled with melted coating material. Excess coating material is wiped away from the surface by doctor blade 25. Roller I3 and doctor blade 26 are automatically maintained at a high temperature suiiicient to keep the material in fluid state as explained above.

After passing the doctor blade, the coating deposit roller surface contains an accurately measured amount of coating material in its recesses and this coating material is deposited as a uniform pattern on the under surface of web 8 as it travels between the pass, formed by rolls l3 and I5. I have discovered that by carefully regulating the pressure of roll l5 upon the upper surface of the web, control may be effected over the amount of material drawn out of the recesses on the deposit roll l3. Preferably roll I! is adjusted to a point where it causes substantially all the material to be drawn out of the recesses without embossing the paper or otherwise injuring it.

The deposited coating material on the web surface immediately chills and hardens and appears in the exact pattern of ridges or mounds in which it has been deposited. The angular relation of thi pattern to the direction of travel of the web is such as to provide the special directional smoothing conditions later to be described.

After passing the depositing station, web S travels through the smoothing station with the coated surface in contact with the free end area of blade 5|. As above described, the tension of web S forces blade 58 to bend and overlie the underlying stationary heated arcuate face 45 which serves as a medial support therefor and defines and controls the curvature of the blade surface which contacts the coated web surface. Thus, the coated surface of the web passes in contact with a smooth, heated arcuate face. Roll 38 may be adjusted to determine the area of contact between the web surface and the arcuate Since roller 45 is maintained at a uniform surface temperature, and due tothe arc of contact of blade 58 with that heated surface, the coating on the web surface is subjected to uniform temperature and pressure and the mounds or ridges of hardened thermoplastic material are now levelled off. As illustrated in Figure 4, the free end of the blade defines with the web surface a subgressively levelled and smoothed .without substantial removal of the deposited material as the web passes over the blade, Due to this arrangement and the arrangement of the pattern of the deposited material, as the ridges or mounds are levelled off. the material removed therefrom is caused to flow upon the web surface in a direction substantially opposite to the direction of travel of the web to fill up the spaces between the ridges or mounds so that this smoothing operation is effected in a controlled manner and provides a smooth uniform coating over the entire web surface.

As shown in Figure 4, the free end of blade 58, after a substantial arc of contact A-B with heated shoe 45, projects further to provide a further flexible smoothing area 3-0 which is not backed by the shoe and terminates at C in a free smooth, straight edge over which the coated surface passes upon leavingthe blade. I have discovered that satisfactory results may be obtained by maintaining a flexible end area B-C about of an inch along the blade and located substantially directly above the center of curvature of the cylinder surface.

Due to the above arrangement, the flexible end portion of the blade is subjected to varying deflection due to changes in tension of the web and other factors. The flexibility of the blade permits specks of dust, lint and other particles to pass through and beyond the edge of the blade and prevents them from accumulating at the edge of the blade and from causing streaking and turbulence in the coating as it leaves the blade edge. This varying deflection is not harmful to the smoothing action since it takes place in a direction substantially on a radius'of the curvature of the blade and normal to the direction of web travel at that point, so that no additional rubbing component between the blade and "web surfaceis introduced. Further while this' varying deflection changes the degreeof contact arc" AB'between the shoe and the blade, it is not sufficient to disturb the heating arrangements ordinarily.

As illustrated in Figure 4, the coated web surface contacts the blade along a portion of area A-B as well as along the area 3-0. For different coating conditions the degree of contact of the coated surface with the areas A-B and B-C may be varied by the blade adjustments at 48 and 51 and by the position of roller 38. In each instance adjustment is effected until the coating leaves the blade edge free of turbulence.

Upon leaving the smoothing surface of the blade, the web passes over the free smooth straight edge of the blade at a selectedslight angle, determined by adjustment of roller 13,

which will give a desired glaze or finish to the surface. This angle depends upon the speed of the web, the nature and thickness of the material being smoothed, and other similar factors. I.

temperature than the coating deposit temperature because the material on the web surface period of time, especially where the web speed is high. This temperature is of course selected according to the-nature of the material of the coating, the web speed, the nature of the paper surface and other factors.

With the web travelling at relatively slow speeds, use of the heated blade is'suflicient for proper smoothing of some materials, but at higher speeds there are many materials which solidify to such a degree between the coating and smoothing stations that they cannot be remelted and smoothed efficiently by a single blade.

Raising the temperature of the blade overcomes this difiiculty with a few of these latter mate rials, but for most of them a blade temperature high enough to remelt them in so short a time would raise them to such a temperature'that they,

would be completely removed from the web surface by the smoothing blade. Accordingly, the blade temperatures must be kept below this dangerous level. I w

By employing heaters 95 and/or 98 to soften the deposited coating immediately prior to contact with the smoothing face of blade 58, or to prevent its solidification after being deposited on ,the web from roll l3, the efficiency of coating This intermediate heating and melting or softening operation greatly lessens the heat which must be supplied by the smoothing blade, simplifies the smoothing operation, and permits the use of higher web speeds. I have also found it desirable to employ heater 85 for softening materials which ordinarily would be satisfactorily smoothed by the blade alone because such presoftening of the deposited coating tends to provide moreuniform temperature conditions in the vicinity of the blade and gives better control over operation of the machine as a whole.

Further embodiments Referring to Figure 9, a further embodiment of the invention wherein different smoothing arrangements are provided is illustrated. Coating material is deposited upon web S in a uniform pattern by substantially the same apparatus as described above in connection with Figure 1. The 1 web then passes in contact with the free end of a spring flexible blade I8, which is preferably of the same construction as blade 58' and is supported along one edge by suitable fastening means indicated at 19 which mounts it loosely upon a rigid support 8| in substantially the same manner that blade 58' is mounted upon its support as above described. Blade 18 is preferably heated by means of a direct heating current through'the blade, an automatically controlled electrical coil, or the like, in holder 8|.

Blade 18 is located as closely as deposit station and is preferably arranged at an angleof about 45 degrees to the plane of the web with itsfree end area bent over by the pressure of the web surface in contact therewith. At

- the area where blade 18 is bent over by the .web,

must be melted and spread within a very short the latter is backed .by roller 82 which is preferably heated and driven in the direction of travel of the web, and the coated web surface is held By elongating the possible mute in contact with the arcuate bent blade surface for a distance of about inch along the blade. Blade 18 is of the same thickness as blade 88. The angle at which the web leaves the edge of blade 18 is slight and may be regulated as by adjustment of a suitable guide roller (not shown) in the same manner as described above in Figure 1.

In Figures 10 and 11, a further embodiment of the coating deposit apparatus is illustrated. A smooth surfaced heated cylinder 83 picks up a continuous coating of thennoplastic material from a bath (not shown but similar to that at 25) and is then wiped by a serrated or uniformly notched doctor bar which is preferably uniformly reciprocated axially of the cylinder to avoid wearing grooves into the cylinder surface and to provide continuous uniformly spaced sinuous ridges of coating material upon the cylinder surface.

Specifically cylinder 83 is engaged along its entire length by a flexible spring steel doctor bar 84 supported in a suitable holder 85. trated in Figure 10, bar 84 is generally wedgeshaped in cross-section and extends through a suitably formed socket in holder 85 to contact the surface of roller 83. bar 84, it is backed by suitable resilient assemblies each comprising a washer 88, a coil spring As illus-- At spaced points along,

81, a second washer 88, and an adjustable screw assembly 88 threaded engaging washer 88 and an end wall of holder 85.

The wiping face of bar 84 is arcuate in section so as to provide substantial line contact between the bar and roller and is notched uniformly, with the size and spacing of the notches of the same order as the size and spacing of the grooves in the grooved coating roller above described. Between each notch 8l is a tooth 82 which bears in wiping contact with the cylindrical surface of roller 83 as illustrated in Figure 11.

As roller 83 rotates, the coating material on its surface is removed in longitudinally spaced bands by teeth 82. After passing the wiping blade, the coating roller surface contains a series of longitudinally spaced rows of ridges 83 of coating material of uniform' size. Due to the slow reciprocation of bar 84, these ridges are sinuous as illustrated in Figure: 11 and of such contour that, when smoothed as by blade 58, flow of the levelled material is against the travel of the web as above described. The deposited material is transferred to the under surface of web S at the pass defined by roller 83 and an impression roller such as that illustrated at l4 in Figure 1. Bar 84 is suitably heated and automatically maintained at the temperature of the coating roller surface.

Holder 85 is preferably rigidly mounted upon the frame so that teeth 82 are in proper wiping contact with the roller surface and movement of bar 84 toward the roller surface is limited by its engagement with its socket on holder 88. Any desired number of the above described resilient backing assemblies may be provided along bar 84, and each is separately adiustable to locally vary the pressure on the bar or compensate for warping of the bar. The above described resilient mounting of the bar permits it to flex and glide over solid impurities which otherwise might destroy teeth 82 if the bar were rigid.

Uniform reciprocation of the bar 84 may be effected by any suitable means such as those now in use for similarly reciprocating ink doctor blades on printing press inking rollers.

Advantages In the above described invention, coating is accomplished in two separate operations, each of which is under control of the operator at all times. During the first part of the process, coating material is deposited upon the sheet or web surface in measured quantities in a uniform pattern. Due to the accurate formation of the recesses on the coating roller surface, only enough material to provide a uniform coating of desired thickness on the web surface is transferred at the deposit station, and since for most purposes a very thin coating is Just as effective as a thick coating, the present invention effects considerable economy in that it enables a uniform coating of minimum thickness to be provided. This manner of controllably and measurably depositing the coating material in a uniform pattern is the essential initial step which enables the second or smoothing operation to be carried out without becoming involved due to piling up of excess material.

The coating material is not only deposited in a uniform pattern by the invention but this pattern is so arranged with respect to the direction of travel of the sheet or web and with respect to the smoothing blade that the smoothing operation effectively comprises a flow of material from the levelled mounds in a direction substantially opposite to that of direction of travel of the webs, and so that no substantial sidewise spreading is required. This controlled flow operation is quite different from merely applying heat pressure and spreading the material at random and is essential for the formation of thin uniform coatings of thermoplastic material.

While the invention, as above described, relates to the complete covering of a surface with a coating of the thermoplastic material, it is possible to effect spot coating by the above described method by providing desired areas of the coating roller with spots or patches of accurately made recesses according to the desired distribution on the surface to be coated. The above described controlled manner of smoothing the deposited material has proved quite effective in retaining the material only in the desired spot areas during smoothing operations.

This invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed and desired to be secured by United States Letters Patent is:

1. In combination, means for depositing melted coating material upon a sheet surface or the like comprising a bath of melted coating material; a roller for transferring measured spaced quantities of said material from said bath to said surface; means for subsequently reheating said coating material on said surface at a surface finishing station to compensate for intervening cooling and solidifying of said material and simultaneously drawing said surface over stationary, smooth curved surface means with said softened coating in contact therewith; and a flexible blade having a straight, smooth edge over which said coataaaaosa ed surface is drawn at an angle selected to give a glazed flnish to said surface.

2. Apparatus for applying a smooth, continuous coating of a material upon a sheet surface or the like comprising means for depositing an accurately predetermined amount of said material as a plurality of spaced mounds upon said surface; and means for levelling said mounds comprising a thin flexible blade supported at one end, a free end portion on said blade and means for drawing said sheet over said blade so as to flex said blade at said end portion in such a manner as to provide a curved blade face of substantiai area in wiping contact with said mounds, said curved blade face terminating in a free edgeover which said coated surface passes upon leaving said face.

3. Apparatus for uniformly and smoothly levelling coating material which has been deposited as a uniform pattern of spaced mounds or the like upon a sheet or web surface comprising a thin, flexible blade supported along one edge in such a manner that it will not distort due to changes in temperature and having an opposite free end area in contact under pressure with said sheet or web surface, said blade end area terminating in a free straight, smooth edge over which said sheet or web passes as it leaves said blade; a smooth, arcuate backing designed to medially support and control the curvature of said blade as it bends in response to the pressure of said sheet or web; and a roller over which said sheet or web passes after leaving said blade edge, said roller being adjustable to determine the angle with which said sheet or web surface leaves said blade edge for obtaining a desired'flnish at said coating.

4. In combination, a bath of coating material, a smooth surfaced cylindrical coating roller at least partly immersed in said bath and an axially reciprocable doctor bar having a serrated surface in wiping contact with said roller surface along its entire length.

5. Thermoplastic coating levelling apparatus comprising a thin, flexible metal blade, a pair of fiat rigid bars arranged along one edge of said blade at opposite sides thereof, a lining of heat insulating material between each of said bars and the adjacent blade surface and fastening means extendingbetween said bars for clamping them loosely but securely upon said blade edge, said fastening means passing through apertures in said blade and said apertures being enlarged to permit expansion of said blade without undesired distortion when said blade is heated.

6. Apparatus for smoothing a coating deposited upon a sheet or web surface comprising a rigid smooth face; a thin flexible blade supported along one edge and having a free end area adapted to be" wipingly engaged under pressure by said surface, said rigid face comprising a medial backing for said blade as the latter is bent in response to pressure of said sheet or web; and means for adjusting said blade support to vary the relation between said blade and said rigid smooth face.

7. In a thermoplastic coating apparatus, a coating station for depositing controlled quantities of tact with said: surface for heating a substantial area of said deposited coating prior to contact wit said smoothing face so that softening of the deposited coating is initiated prior to contact with said heated face.

8. In the thermoplastic coating apparatus defined in claim "I, said means for heating the deposited coating prior to contact with said smoothing face comprising a source of heat and an associated reflector of suflicient size to project said heat over said substantial area of said deposited coating.

9. In themethod of coating a sheet surface or the like wherein controlled quantities of melted coating material are deposited upon said surface and then leveled at a subsequent smoothing station to provide a uniform, smooth coating upon said surface, the step of applying softening heat to said deposited material immediately prior to the levelling operation so that said coating is at least partially softened at the time it initially enters said smoothing station.

10. Apparatusfor uniformly smoothing coating material which has been deposited upon a moving web, comprising a flexible springy blade held at one end in a stationary support and having an opposite free end and means drawing said web under tension over said blade with said deposited coating contacting the blade, said tensed web bending said blade so that said blade and web are in full surface contact over a substantially arcuate area of appreciable extent, and said blade being sufflciently springy to follow said web during changes in web tension and to maintain wiping contact therewith during the smoothing operation.

11. Apparatus for coating a moving sheet or like surface with thermoplastic coating material comprising means for depositing controlled quantitles of said material in melted condition on said surface, a flexible smoothing blade over which said surface is subsequently passed, and heater means maintaining said deposited material softened during its travel between said deposit means and said blade.

12. Apparatus for uniformly leveling coating material which has been deposited upon a surface in ridges or mounds, comprising a member having a rigid smooth face and a flexible surface contacting element supported at one-edge adapted to overlie said smooth face; means for passing said surface under pressure incontact witha predetermined area of said contacting element; and means for restricting vibration of the free end of said element.

13. Apparatus for glazing coating material which has been deposited upon a surface comprising a member having a rigid smooth face; a flexible surface contacting element loosely supported at one edge adapted to overlie said smooth face, and having a flexible straight edge projecting beyond said smooth face: means for passin said surface under'pressure in contact with a predetermined end area of said element and over said straight edge; and means for determining the angle between said surface and said edge.

14. Apparatus for smoothing a coating deposited upon a sheet surface or the like comprising means defining a rigid smooth face; and a thin flexible blade supported along oneedge and having a free end area adapted to be wipingly engaged under pressure by said surface, said rigid face comprising a medial backing for said blade as the latter is bent by pressure of said surface.

15. Apparatus for smoothing a coating which has been deposited as auniform pattern upon a sheet surface or the like comprising a support ate face providing a medial backing support for f said blade as the latter bends in response to pressure of said surface.

16. Apparatus for smoothing a thermoplastic coating deposited upon a sheet surface or the like comprising a heated stationary bar and a thin, flexible blade having high heat conducting properties supported along one edge in such a manner as to prevent distortion due to heat from said bar and adapted to be medially supported by said bar during smoothing operations.

1'7. Apparatus for smoothing a thermoplastic coating deposited upon a sheet surface or the like comprising a bar having a smooth, heated arcuate face and a thin flexible metal blade loosely supported along one edge and adapted to be medially supported and heated by said arcuate face during smoothing operations.

18. Apparatus for uniformly and smoothly leveling thermoplastic coating material which has been deposited upon a sheet surface or the like in a uniform pattern of localized, closely adjacent mounds, comprising a bar having a heated arcuate face; a flexible blade supported at one end and having a sheet surface contacting face of substantial area terminating in a straight, smooth edge at its opposite free end; and means for drawing said coated surface in wiping en-' gagement under pressure with said blade face to level said moimds by causing flow of material therefrom to flll the spaces therebetween substantially in a direction opposite to the direction of travel of said sheet surface, the pressure of said sheet surface forcing said blade to overlie and be medially supported by said arcuate face, and said coated surface being drawn over said blade edge in pre-selected relationship after leaving said blade face.

19. In the apparatus defined in claim 18, said blade being loosely supported at said one end to prevent distortion thereof due to heat from said arcuate face.

20. Apparatus for leveling thermoplastic coating material which has been deposited upon a sheet surface or the like in a uniform pattern of localized, closely adJacent mounds comprising a bar having a smooth, heated arcuate face; a thin, flexible blade supported at one end and having a sheet surface contacting face of substantial area terminating in a straight. smooth edge at its opposite free end; means for drawing said coated surface in wiping engagementv under pressure with said blade face so as to provide an appreciable length of contact between said blade face and said coated surface along the .line of travel of said coated surface, said blade being medially supported by said arcuate face as it is bent by pressure of said coated surface and said blade being disposed transversely of the line of travel of said coated surface and in such relation to said pattern that material from the leveled mounds is caused to flow into the spaces between said mounds in a direction generally opposite to the direction of travel of said coated surface.

21. In apparatus for coating a web surface, means comprising a roller provided with a uniform pattern of surface recesses of known size for depositing controlled quantities of coating material upon said surface, a flexible blade supported at one edge and having a rigid backing provided with smooth curved face means underlying and loosely supporting the blade intermediate its ends, said blade having a straight smooth edge at its free end, means for drawing the web under tension over said blade with the deposited material in contact 'with said blade over a substantial area and said web passing over said smooth edge in a manner selectedto give a predetermined finish to said coating.

22. A device for polishing or glazing coating material deposited on a sheet surface or the like from an engraved plate or cylinder, comprising a thin, flexible springy blade, supported at one edge in such a manner that when heated it can expand without distortion; backing means supplied medially of said blade, said backing means being heated to control the temperature of the blade; and means for bringing the coated sheet surface into flexible contact under pressure over a considerable area of said flexible heated blade, and then drawing said surface of! the free true edge of said blade after leaving said area, all in such a manner as to avoid creating turbulence in the coating.

23. Apparatus for uniformly smoothing coating material which has been deposited upon a moving web, comprising a flexible springy blade held at one end in a stationary support and having an opposite free end, means drawing said web under tension over said blade with said deposited coating contacting said blade, said tensed web bending said blade so that said blade and web are in full surface contact over a substantially arcuate area of appreciable extent, and said blade being sumciently springy to follow said web during changes in web tension and to maintain wiping contact therewith during the smoothing operation, and a free, sharp, smooth flexible terminal edge on said blade over which the coated surface of said web is drawn at a a selected angle beyond said area.

24. Apparatus for uniformly smoothing coating material which has been deposited upon a moving web, comprising a flexible springy blade held at one end in a stationary support and having an opposite free end, means drawing said web under tension over said blade with said deposited coating contacting the blade, said tensed web bending said blade so that said blade and web are in full surface contact over a substantially arcuate area of appreciable extent, and said blade being sufficiently springy to follow said web during changes in web tension and to maintain wiping contact therewith during the smoothing operation, and means for heating said blade.

25. In the apparatus deflned in claim 24, said means for heating the blade substantially uniformly heating that portion of the blade which is engaged by said web.

26. Apparatus for applying a smooth, continuous coating upon a sheet surface or the like comprising a roller having a plurality of accurately formed surface recesses of known size for depositing predetermined quantities of fluid coating material as closely spaced relatively small localized mounds on said surface; and means for levelling said mounds comprising a thin flexible blade supported atone end, a free end portion on said blade and means for drawing said sheet over said blade so as to flex said blade at said end portion in such a manner as to provide a curved blade face of substantial area in wiping contact with said mounds, said curved blade face terminating in a free edge over which said coated surface passes upon leaving said face.

2'7. Apparatus for applying a smooth, contin- 5 uous coating of thermoplastic material upon a sheet surface or the like comprising means for depositing an accurately predetermined amount of said material in fluid condition as a plurality of spaced mounds on said surface; and means for levelling said mounds comprising a heated thin flexible blade supported at one end, a free end portion on said blade and means for drawing said sheet over said blade so as to flex said blade at said end portion in such a manner as to proport, a free end portion on said blade and means drawing said sheet over said blade so as to flex said blade at said end portion in such a manner as to provide a curved blade face of substantial area in wiping contact with said deposited coating, said curved blade face terminating in a. free edge over which said coated surface passes upon leaving said face.

29. In combination, a smooth faced member over which a sheet having a quantity of coating material deposited upon a surface thereof is adapted to pass with the uncoated surface of said sheet in 61058 contact with said member, and a flexible blade defining a smooth straight edge for subsequently contacting the coated surface of said sheet at an angle selected to give a glazed finish to said coated surface.

Apparatus for treating a sheet surface comprising a rotatable cylinder contacting a substantial area of said sheet on the side oppo- 0 site the surface to be treated, and a flexible blade having a smooth straight edge contacting said surface to be treated adjacent said cylinder at a predetermined angle.

JOHN D. MURRAY. 

